The present invention relates to a rock anchor assembly. It particularly relates to a rock anchor assembly comprising a tensioning element adapted to be inserted into a bore hole and to be clamped therein, the outer end of which projecting from said bore hole being adapted to be tensioned against a rock wall by means of an anchor plate. The invention also relates to a method of installing said rock anchor in a wall.
German Offenlegungsschrift 2 624 559 of the present inventor discloses a rock anchor assembly of the above type wherein the tensioning element is formed of a steel pipe, the outer end of which is threaded so that a clamp nut may be secured thereon. Reinforcing elements in the form of glass fiber--synthetic resin rods are inserted into the steel pipe. The rock anchor is installed in a bore hole formed in a wall by means of a liquid synthetic resin. After hardening of the injected liquid resin the anchor assembly is tensioned against the wall with the aid of the anchor plate using said clamp nut.
These known rock anchors have proven to be effective in practice, because in view of the hardenable resin they may be installed in a bore hole in a relatively simple manner. Further they may be put under tensile stress by means of the clamp nut and the anchor plate so that the rock materials overneath are securely fastened.
It is an object of the invention to provide a rock anchor comprising only a small number of pre-fabricated parts which in accordance with the particular requirements may be assembled at the construction site, which rock anchors may also be anchored in a rock material without an indispensable need of injecting synthetic resin.
It is another object of the invention to provide a method of installing a rock anchor in a wall using said rock anchor assembly.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The above objects are achieved according to the invention by the provision of a rock anchor assembly comprising a tensioning element adapted to be inserted into a bore hole and to be clamped therein, the outer end of which projecting from said bore hole being adapted to be tensioned against a rock wall by means of an anchor plate, the inner end of said tensioning element inserted into the bore hole being provided with a spreading jacket clinging into said bore hole and being adapted for tensioning with the inner end of the tensioning element by means of a spreading wedge upon turning a clamp nut, and wherein said clamp nut is secured on a threaded tensioning jacket adapted for tensioning with the outer end of said tensioning element with the aid of tensioning wedge means upon turning the clamp nut.
A substantial advantage of the rock anchor according to the invention is that it features a simple construction. Thus, according to the particular requirements at the place of application of the rock anchor the smooth tubular tensioning element, which does not require a thread for securing the clamp nut, is cut to the required length. Thereafter the spreading means comprising a spreading jacket and a spreading wedge are positioned onto the inner end. The tensioning means, comprising a tensioning jacket, a tensioning device, for example a tensioning wedge, a clamp nut and the anchor plate are placed on the outer end of the tensioning element. In spite of this simple construction of the rock anchor, which may be assembled exceptionally fast and economically, it provides an excellent hold in rock walls, because the spreading jacket, which on its outer surface is provided with barbs or similar projections, clings fast in the bore hole.
According to a preferred embodiment of the invention the tensioning element has a tubular configuration with both ends of the tensioning element being adapted to be conically widened and both being provided with cross wedges with an axial injection bore for introducing a filling material.
According to this embodiment of the rock anchor in those cases, where an anchoring with the aid of the spreading jacket in the bore hole may not be sufficient, a hardenable synthetic resin may be injected through the cross wedge positioned on the outer end, whereby the anchoring in the bore hole is further improved.
According to another preferred embodiment of the invention the ends of the tensioning element, which may be conically widened, are provided with crosswise positioned slots while the cross wedges or spreading wedges have a radial shape such that their arms or projections engage into said slots.
This embodiment of the cross wedges or spreading wedges has the advantage that with increased tensile stress the the material of the tensioning element will not penetrate into the slots which would impair the secure functioning of the rock anchor.
Instead of the tensioning wedge being positioned between the conically tapered inner end of the tensioning jacket and the essentially cylindrical end of the tensioning element, the tensioning device may consist of the conically widened end of the tensioning element and an opening in said tensioning element paired therewith being of conical shape on at least part of its length. This alternative construction has as an advantage that the outer surface of the tensioning element may have a cylindrical form over its entire length and may thus be provided with a very long thread. Also, the injection bore of the cross wedge directly located at the head of the rock anchor is exposed so that an easier operation is possible.
According to a further feature of the invention the tensioning element may have the form of a smooth glass fiber reinforced synthetic resin pipe. The advantage resulting therefrom is that a very light and easily transportable material for the tensioning element is provided which at the construction site may easily be cut to the desired length. No reduction of the tensile strength of the rock anchor assembly will result therefrom. Instead of the smooth glass fiber-synthetic resin pipe it is also feasible to use a roughened glass fiber reinforced synthetic resin pipe.
According to an alternate preferred embodiment of the invention the tensioning element is of a solid configuration, i.e. has the form of a rod. This construction is particularly useful, if the rock anchor is intended for applications which involve a particularly high tensile stress. If the tensioning element has the form of a rod, it is preferred that tensioning shells are put onto both ends of the tensioning element. It is also possible to form the rod-like tensioning element such that both ends thereof are provided with crosswise slots into which correspondingly shaped cross wedges are inserted.